Navigation Links
Nervous system

The nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and processes input from the senses, and initiates actions. (see Central Nervous System).

In animals with brains, the nervous system also generates and conducts thoughts and emotions. Thus it is the system that animates "animals" (sponges are an exception). Chemicals that target the activity of nerves generally are the most rapidly acting toxins, typically causing paralysis and/or death.



The nervous system consists basically of two types of cells:

  • Neurons are the primary cells of the nervous system
  • Glia are secondary cells involved in nourishment and structural support.

Rapid signalling within the nervous system occurs by two primary mechanisms:

Vertebrate nervous systems

The nervous systems of vertebrate animals are often divided into a central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists of all other nerves and neurons that do not lie within the CNS. The large majority of what are commonly called nerves (which are actually axonal processes of nerve cells) are considered to be PNS. The peripheral nervous system can also be roughly seen as consisting of sensory pathways and motor pathways , the latter being divided into the somatic (voluntary) nervous system and the autonomic nervous system.

The somatic nervous system is the voluntary part of the nervous system that coordinates a body's movements, such as maintaining a particular posture and walking. The autonomic nervous system is the involuntary part of the nervous system where all of the internal maintenance is taken care of.

The autonomic nervous system is then divided into the sympathetic division and parasympathetic division. The sympathetic nervous system responds to impending danger or stress, and is responsible for the increase of one's heartbeat and blood pressure, among other physiological changes, along with the sense of excitement he feels. The parasympathetic nervous system, on the other hand, is evident when a person is resting and feels relaxed, and is responsible for such things as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels, and the stimulation of the digestive and geniturinary systems.

Nervous system diversity

The nervous system varies greatly among living animals. Cnidarians, such as sea anemones and jellyfish, have a nerve net, in which the activation of any one neuron triggers a wave of activation across the entire network. These waves are both afferent and efferent, representing both the sensation of chemicals or touch as well as the stimulus of the animals' reflexive mechanical response.The worms and flukes of the phylum platyhelminthes possess a network of nerves that operates like a more conventional nervous system, but lack a brain. Annelid worms and tunicates have a primitive brain called a ganglionic mass, which is a bundle of several nerves. Based in part on commonalities in embryonic development among all chordates, the tunicate brain is believed to resemble the evolutionary precursor of the vertebrate brainstem.

See also


(Date:9/2/2014)... hot oven, you rapidly pull your hand away. Although ... and responding to such painful stimuli, they are still ... made a surprising discovery about the role of a ... built a structural model of the molecule. These discoveries, ... help direct new strategies to treat pain in people. ...
(Date:9/1/2014)... wisdom has long held that corals whose ... are passive organisms that rely entirely on ... nutrients and oxygen. But now scientists at MIT ... Israel have found that they are far from ... turbulent patterns that greatly enhance their ability to ...
(Date:9/1/2014)... animals, bats are perfectly adapted to a life without light. ... reflected echoes to measure distance to obstacles or prey. In ... delays. A study carried out by researchers at Technische Universitt ... map dynamically adapts to external factors. , Closer ... in too close to an object, the number of activated ...
Breaking Biology News(10 mins):Surprising new role for calcium in sensing pain 2Surprising new role for calcium in sensing pain 3Nature's tiny engineers 2Nature's tiny engineers 3Zooming in for a safe flight 2
... deaths are due to metastasis, the spread of cancer cells ... These metastatic cells tend to move more than their non-metastatic ... cancer cells intently with the hope they can learn to ... researchers now have demonstrated a novel and simple method that ...
... CLEVELAND Studying how the mouth wards off diseases ... healthy. The Case Western Reserve University School of ... from the National Institutes of Health,s National Institute for ... dental school,s 117-year history to study oral health as ...
... Scientists from the Helmholtz Center for Infection Research in ... succeeded in treating immune cells in a way that ... organ rejection. Their results have now been published in ... of Cellular and Molecular Medicine . The immune ...
Cached Biology News:New method separates cancer cells from normal cells 2NIH funds $9.5 million for research on HIV and the human innate immune system 2NIH funds $9.5 million for research on HIV and the human innate immune system 3NIH funds $9.5 million for research on HIV and the human innate immune system 4GARP makes the difference 2
Other biology definitionOther Tags